Adrenoceptor interconversion from beta to alpha was observed in myocardium during hypothermia or hypothyroidism and this results in enhanced alpha adrenoceptor activity during stimulation with norepinephrine and similar drugs. Thus far, interconversion has been demonstrated only in myocardium, but if it were shown in vascular smooth muscle during hormone homeostasis imbalances, it may gain pathophysiologic significance as a possible contributor to development and maintenance of hypertension. Initially, this study will use known methods which acutely produce interconversion (hypothermia and metabolic inhibitors) to assure that the phenomenon occurs in vasculature. Imbalances of thyroid hormone, adrenocortical steroids and sex hormones will be induced to determine whether increased noradrenergic responsiveness seen in these conditions is due to interconversion. Aortic tissue will be obtained from each animal when the condition is established, then responsiveness to vasoconstricting and dilating sympathetic agonists will be studied in the absence and presence of specific antagonists. Cumulative log concentration-response curves will be obtained for comparing agonist potency and efficacy and antagonist activity (pA2 and KB) from one condition to another. These curves will be examined for potency or efficacy changes indicative of enhanced alpha or beta adrenoceptor activity, then these data will be compared to changes in pA2 which may be suggestive of adrenoceptor alteration. Finally, changes observed with the above parameters will be compared to receptor labeling studies with 3(H)-phenoxybenzamine. Parallel changes in both sets of data should be evidence of adrenoceptor interconversion. In adrenoceptor interconversion is demonstrated in vasculature and associated with increased vasoconstriction with lost vasodilation, these findings might be used as the basis for thorough hormone profiling and and subsequent management of imbalances as adjunctive therapy for more specific and effective management of these selected forms of hypertension.